1. Field of the Invention
This invention relates to a stereomicroscope capable of varying magnification.
2. Description of the Prior Art
A stereomicroscope which enables microscopic parts to be viewed stereoscopically is widely used for measurement during the performance of precision machining in the manufacturing industry and for making accurate observations of affected parts, increasing the securing of operations, and enhancing the safety of patients in the medical industry. A conventional stereomicroscopic, however, has the problem that since a viewer's posture for observation, namely, the position of a viewer's eyes (which is hereinafter referred to as "eyepoint") where the viewer observes an image through the microscope, is restricted because of the structure of the stereomicroscope, the image will disappear from view with a slight change of the posture. Consequently, when such a stereomicroscope is used to work over a period of long hours, a viewer must pay attention to his posture for observation in such a manner that the eyepoint is not moved during the work, and thus fatigue is increased.
To lessen such fatigue, an optical arrangement is proposed that, as set forth, for example, in U.S. Pat. No. 4,671,628 (see FIG. 1), the distance between rays of light for observation 2 and 2' emerging from an objective lens 1 is increased and adjusted by movable mirrors 3 and 3' and a fixed mirror 4 so that the distance between the exit pupils at an eyepiece 5 can be controlled with great ease and a field lens 7 is disposed to make the distance between the exit pupils larger than that between the eyes of a viewer 6 for easy observation.
This arrangement, however, needs a proper adjustment for the distance between the exit pupils to obtain a fair image whenever the viewer changes, and does not enable the viewer to change the eyepoint at will in a direction of easy observation during the observation because the eyepoint is restricted.
Hence, it has the problem that, when precision work is carried out over a long time, notably, in turn by a plurality of viewers, the distance between the exit pupils, the direction of observation, and the eyepoint must be finely adjusted and corrected to the viewer's own liking, with resultant complicated operation. Further, there is another problem that its complicated structure makes the working position far from the eyepoint, thus reducing work efficiency.